1. Field of the Invention
This invention relates to an internal combustion engine mounted on a personal watercraft for operation in water. More particularly, this invention relates to an internal combustion engine having an improved cooling system configuration.
2. Description of the Background Art
The personal watercraft, or small-sized planing boat, is constructed such that an internal combustion engine for driving a jet propulsion pump is mounted in a boat body enclosed by a hull and a deck. A driver and up to two other crew members rides on the deck, so that an in-boat space, constituted by the hull and the deck, is narrow. The internal combustion engine is stored in a substantially closed and sealed state within the narrow space between the hull and the deck.
As a consequence, a compact internal combustion engine is required. In order to minimize the height of the internal combustion engine, a dry sump having no oil reservoir for accumulating a large amount of oil is employed. Such an internal combustion engine is disclosed, for example, in JP-A No. 2003-35201.
The oil passage of the dry sump in JP-A No. 2003-35201 is provided with a water-cooled type oil cooler so as to restrict an increase in temperature of the lubricant oil. In the personal watercraft, cooling water fed from the positive pressure side of the jet propulsion pump is used for cooling the internal combustion engine, and the oil cooler also utilizes this cooling water.
The oil cooler disclosed in JP-A No. 2003-35201 is stored in an oil cooler housing arranged longitudinally side-by-side with the oil tank at the front part of the internal combustion engine. The oil is cooled by means of cooling water which flows through the oil cooler housing about the oil cooler.
The oil cooler housing is a vertically elongated unit extending from the upper part of the cylinder block to the lower part of the crankcase. In particular, the lower part of the oil cooler housing, at the location where the cooling water flows in, is near the bottom surface of the personal watercraft, has no surplus space and is set at substantially the same height as that of the jet propulsion pump. Accordingly, cooling water fed from the positive pressure side of the jet propulsion pump to the oil cooler storing part is not necessarily discharged out of the positive pressure side of the jet propulsion pump, even if personal watercraft is pulled up onto land. As a result, it is possible that cooling water remains in the oil cooler housing of a dry-docked vessel.
The present invention has been invented in view of the above described problems. It is an object of the present invention to provide an internal combustion engine for a personal watercraft in which cooling water in the oil cooler housing is naturally discharged when the personal watercraft is pulled up on land.